2 Answers
2

I suggest you first try to add a logging rule just before the one you wrote; something like:

iptable -I INPUT 1 -p tcp --dport 3343 -j LOG;

this way you can monitor if the traffic is actually getting to your server; if the traffic is actually getting to your server, take a look at the outgoing packets; maybe packets reach your application, but they can't travel back because of routing tables or anything else; if you can confirm the incoming packets get to your application, try with:

iptables -I INPUT 1 -p tcp --sport 3343 -j LOG

THis way you can monitor which kind of packets, if any at all, your application is sending out, and through which inteface.

Also, I assume you've no nat in place, so the iptables -t nat --list -n is empty.